1. Field of the Invention
The present invention relates to a portable apparatus having a head retracting function for detecting a drop of an apparatus to retract a head, and a head retracting method.
2. Description of Related Art
Recently, a hard disk drive (HDD) has progressed to have a large capacity and a small size, and accordingly various electronic apparatus have adopted HDDs.
In particular, the HDD are widely adopted by AV apparatus such as a video camera, a video recorder, audio recorder/player and the like by making use of the feature of having a large capacity. Moreover, owing to the progress of the miniaturization thereof, the HDD is also used for portable AV apparatus.
Now, the HDD is configured to make the magnetic head thereof float at the time of reproducing or recording data from or to the hard disk thereof by rotating the hard disk to roll in the air between the magnetic head and the hard disk. Consequently, when the power supply thereof is abruptly interrupted to stop the rotation of the hard disk, the air is not rolled in between the magnetic head and the hard disk. Then, the magnetic head is contacted with the hard disk to cause disadvantages such as injuring the recording surface thereof to break recorded data and damaging the head.
To avoid such disadvantages, many HDDs are severally equipped with an auto-retraction function for retracting the magnetic head thereof to a position where the magnetic head is not opposed to the hard disk thereof when the power supply thereof is interrupted.
Moreover, in the case where the magnetic head located at a position opposed to the hard disk collides with the hard disk owing to an impact, for example, at the time of a drop of the apparatus, there are the cases where the recording surface of the magnetic disk is significantly injured, recorded data is broken, or the magnetic head is damaged. In particular, in the case where a HDD is built in a portable apparatus, the danger of a drop is large.
Accordingly, some portable electronic apparatus and the like severally plan to protect the HDD thereof from the impact by being provided with, e.g. a mechanical damper, and are adapted to perceive a drop for turning off the operating power supply thereof to be supplied to the HDD, and thereby to retract the magnetic head thereof to a position where the magnetic head is not opposed to the hard disk thereof by means of the auto-retraction function thereof for avoiding a break of the HDD by a drop impact which only the mechanical damper cannot deal with.
In this case, as a method for perceiving the drop, there has been proposed a method for detecting the drop by obtaining the magnitude of a synthesized acceleration vector obtained by detecting acceleration at least in three directions located not on the same plane (or each direction of an X-axis, a Y-axis and a Z-axis, all perpendicular to one another) to synthesize the detected acceleration, and by detecting the magnitude of the synthesized acceleration vector to be stabilized at a value near in the neighborhood of 0 G for a predetermined time to perceive the drop. For example, the method is also disclosed in the below Patent Document 1.
According to the method, a free drop of the HDD from an upper position by 25 cm which is regarded as a limit of the height from which the HDD can drop without being broken is supposed, and the portable electronic apparatus is judged to be dropping when the time during which the magnitude of the synthesized acceleration vector is stable near to 0 G is equal to or longer than a predetermined time (e.g. 100 ms). Then, the magnetic head is retracted to a position where the magnetic head is not opposed to the hard disk.
[Patent Document 1] Japanese Patent Publication No. 3441668
However, the following problem remains in the method described above.
In the case where a vector sum of each direction of the X-axis, the Y-axis and the Z-axis is calculated to be detected near to “0 G” and the value of the vector sum has continued for a predetermined period, a drop is judged, as described above. However, the detection is an accurate judgment only under an ideal condition. The ideal condition means a state in which an acceleration sensor (G sensor) for detecting each piece of acceleration of the X-axis, the Y-axis and the Z-axis is located at the center of gravity of the apparatus and the apparatus is dropping without rotating. The situation is described with reference to FIGS. 5 and 6.
FIG. 5 shows an example of the outputs of a G sensor, i.e. the respective sensor outputs of the X-axis, the Y-axis and the Z-axis, and a vector sum in the sate in which the apparatus is stationary. In the stationary state, each sensor output of each axis indicated by a broken line takes a constant value. In this example, the sensor outputs of the X-axis and the Y-axis is near to 0 G, and the sensor output of the Z-axis is near to 1 G. Incidentally, each value of the sensor outputs of each axis in the stationary state depends on the posture of the apparatus at that time.
Then, the vector sum of the X-axis, the Y-axis and the Z-axis is 1 G as shown by a solid line.
Incidentally, a detection time t1 is set to, e.g. about 100 ms. If the vector sum is near to 0 G continuously during the detection time t1, the state is judged to be a drop in a period t2, and a head retracting operation is performed in a period t3. In the case of FIG. 5, the vector sum is stable at 1 G, and consequently the state is not judged as a drop.
FIG. 6 shows a variation of a vector sum in the case where the apparatus dropped in the ideal state described above.
As shown in the drawing, the value of the vector sum begins to lower immediately after the beginning of a drop, and takes a value of almost 0 G during the drop. In this case, because the vector sum is near to 0 G continuously during the period t1, the state is judged as a drop during the period t2, and the head retracting operation is performed during the period t3.
However, in a nonideal state, the state is not always as the one shown in FIG. 6. That is, the nonideal state is a case where the G sensor is not located at the center of gravity of the apparatus, or a case where a rotation operation accompanies the operation of dropping at the time of the drop.
FIG. 7 shows a vector sum at the time of a rotating drop. Also at the time of the rotating drop, the value of the vector sum is stabilized to a certain value. But the value at the stable state is not always near to 0 G. The case where the vector sum takes the value shown in FIG. 7 is only an example of the values depending on the rotation state and the location position of the G sensor. In the case where the value of the stable state becomes distant from 0 G (becomes near to 1 G), the state is not detected as a drop.
In particular, lest the drop should not be easily judged to perform the retraction operation unnecessarily frequently, a dead zone, which is shown by alternate long and short dash lines, is provided near to 1 G to regard the values in the dead zone as 1 G. When a vector sum at the time of a drop is stabled within the range of the dead zone, no drop judgments are performed in spite of dropping. That is, no retraction operations can be performed.
FIG. 8 shows a case where a vector sum is stabilized near to 1 G at the time of a rotating drop. There is the case where the vector sum stays near to 1 G like that by the variation of each sensor output of the X-axis, Y-axis and the Z-axis as shown by broken lines at the time of the rotating drop. In this case, such a state is not judged to be a drop, and head retraction is not performed. Consequently, there is the possibility that the HDD is broken by a drop impact.
In consideration of HDD player/recorder as a portable apparatus, the miniaturization of the apparatus is important. Owing to the restriction of the mounting of the internal constitution for the miniaturization, there are many cases where a G sensor cannot be disposed at the position of the center of gravity of the apparatus. Moreover, in case of considering the status of use as a portable apparatus, it is expected that rotating drops occur frequently.
That is, there is a problem in which the prior art method of judging a drop by a vector sum being near to 0 G for a predetermined time cannot sometimes suitably judge a drop and is particularly not suitable for portable apparatus.
On the other hand, it is also considerable to provide rotation detecting sensor separately for detecting a rotating drop, but mounting the rotation detecting sensor causes the difficulty of miniaturization, an increase in cost, and the like, and it is especially disadvantageous to portable small-sized apparatus.